1. Field of the Invention
The present invention relates to an information processing apparatus capable of transmitting/receiving a data stream via a network, a method of controlling such an information processing apparatus, an information processing system, and a computer-readable memory.
2. Description of the Related Art
If a certain kind of fluorescent substance is irradiated with a radiation (such as X-rays, alpha rays, beta rays, gamma rays, electron rays, or ultraviolet rays), the energy of the radiation is partially stored in the fluorescent substance. If this fluorescent substance is excited by light, such as visible light, the fluorescent substance emits stimulated fluorescent light depending upon the stored energy. This type of fluorescent substance is called a storage fluorescent substance (stimulated fluorescent substance). It is known to temporarily record a radiation image of a subject such as a human body on a storage fluorescent sheet and obtain an image signal by illuminating the storage fluorescent sheet with stimulation light such a laser beam, so as to generate stimulated fluorescent light and opto-electronically read the generated light.
Japanese Patents Laid-Open Nos. 55-12429 and 56-11395 disclose a radiation image recording/reproducing system in which a radiation image of a subject is output in the form of a visible image on a recording medium, such as a photographic recording medium, or on a display, such as a CRT, in accordance with an image signal obtained from stimulated fluorescent light.
In recent years, there has been developed an apparatus for acquiring a visible image from an X-ray image using a semiconductor sensor. Such systems have the advantage that an image can be formed over a very wide exposure range compared with a conventional radiation photography system based on the silver halide photography. More specifically, X-rays are detected by an optical-to-electric signal converter over a very wide dynamic range and a corresponding electrical signal is output. A visible image corresponding to the radiation image is formed on a recording medium such as a photographic recording medium or on a display such as a CRT in accordance with the electrical signal. This makes it possible to obtain a radiation image without encountering a problem caused by a variation in exposure.
When an image is stored or transmitted, the data size of the image is reduced by means of high-efficiency coding. More specifically, the data size of the image is reduced by removing redundancy in the image or changing the content of the image within a range in which significant visible degradation does not occur.
According to the JPEG standard, which has been recommended by ISO and ITU-T as an international standard for coding a still image, differential pulse code modulation (DPCM) is employed for reversible compression, and discrete cosine transform (DCT) is employed for irreversible compression. For detailed information about the JPEG standard, refer to the ITU-T recommendation T.81 ISOIEC 10918-1.
In recent years, a compression method using a discrete wavelet transform (DWT) has been developed. This method is known as JPEG2000. In contrast to the compression method such as the JPEG compression method based on the DCT, the compression method based on the DWT has the advantage that blocking artifacts do not occur.
In medical applications, images are needed to be stored as a medical care record in the form of a lossless data for a certain period of time. To meet such a requirement, the JPEG2000 method supports lossless coding based on the DWT. However, although this lossless coding technique has the advantage that an image having certain image quality can be formed from a starting part of a file, the problem is that the compression ratio is as low as about 1:3.
In a computer network environment, although the processing capacity and the storage capacity of a computer can be easily improved, a network having a low transmission rate results in a great reduction in the overall processing capacity of the system. If there is only one such a low-speed network, this network can cause a bottleneck.